SOME PHYSIOLOGY YOU OUGHT TO KNOW 23 



were of little value. The animal could not use 

 them for food, they could not be burned to furnish 

 heat, and they stored up no energy to carry on any 

 of the world's work. What a change the plant 

 makes of them! So used, they become the source 

 of the animal food, and, as food, they contain five 

 principal groups with which the animal is nour- 

 ished. These five groups are the air, water, the 

 protein compounds, the nitrogen free compounds, 

 such as starch, crude fiber, sugar and gums, and 

 the fat or ether extract, as it is called. 



DIGESTION OF THE FOOD 



Before these different constituents of the plant 

 can be used as food for animals, they must be pre- 

 pared for absorption into the system of the animal. 

 This preparation takes place in the mouth, oesoph- 

 agus tube, the stomach, and the intestines, aided 

 by the various secretions incident to digestion and 

 absorption. Any withholding of any essential con- 

 stituent has its result in inefficiency or illness of 

 the animal. 



Withhold ash materials, for instance, from the 

 food, or supply an insufficient quantity, and the 

 fact will be evidenced by poor teeth, deficient bone 

 construction and poor health in general. Let the 

 feeding ration be short in protein, and the result 

 will be shown in the flesh and blood. Let the car- 

 bohydrates and fat be withheld or supplied insuf- 

 ficiently, and energy will be denied and a thrifty 

 condition will not be possible. 



The supply of these different constituents in the 

 proper proportion gives rise to the balanced ration ; 

 and is concerned in a treatise of this kind only in so 

 far as it has to do with disease or health. For, 



